Secondary dispersion from gold deposits in west Turkey

Orientation studies over the Sarpdag prospect in the Biga peninsula and the Arapdagi deposit near Izmir have provided clear evidence for elemental dispersion around west Turkish gold prospects. Although these deposits are of different types, silicification associated with the deposits results in the main part of both deposits forming topographic highs. At Sarpdag gold mineralisation is relatively weak compared with nearby prospects and associated with a silicified cap on the main hill. Comparison of coarse and fine fractions, based on a 190 mu m size split of 8 kg of -2 mm material, suggests that gold disperses elastically on the steep slopes, probably within silica, but coarse grains break down giving Au concentrations in the finer fractions at the base of the main slope. Discrete gold grains, that can be panned, only occur 1-2 km downstream within the streams and heavy mineral concentrations are very limited. This interpretation of Au dispersion is consistent with the data from 1 kg samples collected at the higher primary grade, but more contaminated, Arapdagi prospect. Antimony is the most consistent pathfinder both for the silicified cap at Sarpdag and for gold-rich veins at Arpadagi. It gives high contrast anomalies. Arsenic is useful being more mobile than Sb, although contrast may be low. High resolution Ag data can be useful but base metal enrichments are also often associated with Ag anomalies. Most prospects have some base metal enrichments although they can be displaced from the main gold-rich parts of the deposit and anomalies may be weak. Lead and Cu are the more consistently useful elements. The use of large (> 8 kg of -2 mm material) samples produces consistent stream sediment data that can be used to reliably interpret single samples and quantify Au anomalies. A survey around the Halikoy Hg and Emirli Sb mines, using these large samples, confirmed the extension of the known gold-bearing Emirli structure. In contrast the major Hg-bearing Halikoy Fault is gold poor although a structure parallel to it is auriferous.